Reactor for high-temperature cracking



Patented July 7, 1953 REACTOR FOR HIGH-TIWPERATURE CRACKING Karl T. Hartwig, Glen Ellyn, and Charles H. Watkins, Western Springs, Ill., assignors to Universal Oil Products Company,

corporation of Delaware Application February 26, 1951, Serial No. 212,744 i Claims.

The present invention relates to an improved reactor for eiecting high temperature cracking, and particularly for providing rapid mixing and high temperature conversion of gaseous reactant streams under controlled conversion conditions.

A gas mixing and contacting apparatus or reactor, of the present type, may be used to advantage in many types of high temperature cracking or conversion operations. For example, the present reactor may be used to advantage in carrying out the autothermic or oxidative cra-cking of volatile hydrocarbon streams to produce ethylene, or other desired olens, dienes, and the like. Also, a low molecular Weight hydrocarbon stream such as propane may be preheated and mixed with preheated air or oxygen to effect the autothermic cracking of the propane into aA product stream having a relatively low density and heating Value making it desirable for use as a fuel gas or a supplementary send-out gas which may be used by companies to meet peak load demands. The efficiency of the autothermic process is primarily dependent upon the use of desirable form of apparatus which effects a rapid mixing and contacting of reactant gaseous streams, as well as means for controlling reaction time andtemperature. Further, a desirable form of apparatus or reactor used in autotnermic cracking, to eect high thermal eiciency, provides for heat exchange hows, whereby preheating of the reactant streams may be effected, and particularly the continuous preheating of reactant streams by a recuperative heating from a resulting product stream.

It is a principal object of the present invention to provide an autothermic or oxidative cracking type of reactor which is of a relatively simple design land construction, and has means for effecting recuperative heating so that the gaseous charge streams are preheated by a resulting gaseous product stream.

-It is also an object of the present invention to provide an apparatus having the reactor chamber enclosed by and combined with an external heating chamber which provides a desirable means for insulating the reactor, and for providing' operating temperature control, as Well as starting-up temperature control.

It-is still a further object of the present invention to provide a compact design and construction Chicago, Ill., a

2 for an externally heated and recuperative type of autothermic reactor which provides a high thermal elciency 'and may be readilyassembled or disassembled for maintenance purposes.

Briefly, the present form of compact autother-` mic cracking reactor comprises in combination, an elongated pressure tight chamber having a refractory tubular member spaced concentrically and longitudinallytherein, the tubularr member being spaced from inner wall of the chamber' and forming an annular shaped gasA passageway therewith, a closed end and an open end to the tubular member and an elongated and axially positioned hollow portion therein forming a reaction section which is in open communication with the interior of the pressure tight chamber through the open end of the tubular member, a reactant stream inlet and an'air inlet connecting with the pressure tight chamber at the end thereof adjacent to the' closed end 0f the refractory tubular member therein, pipe coils extending from the inlets and positioned around the refractory tubular member within the annular shaped' gas passageway, the pipe coils extending tothe end of the tubular member having Ythe open end therein and connecting with conduits extending longitudinally'through the body of the tubular member to a mixingchamber positioned within the closed end of the tubular member, with the mixing chamber having ports therein connecting with the gas conducting conduits and discharging into a mixing throat, the latter connecting to and n discharging through a ared portion `of the mixing chamber into the axially positioned reaction section ofv the tubular member, whereby the resulting mixed gases and product stream may pass longitudinally through the reaction section and from the open end thereof into the kenclosed chamber and reverse its flow to pass through the annular gas passageway in heat exchange relationship with the pipe coils positioned therein, product gas outlet means from the pressure tight chamber at the inlet end thereof, an enclosed and insulated heating chamber circumscribing and spaced from thepressure tight chamber forming an annular heating section therearound, gas

burner and fuel supply means at one end of the heating section and adjustable air inlet means through the `external'heating chamber adjacent' the burner means, and ue gas outlet means through the heating chamber at an end opposing the positioning of the burner means whereby hot flue gases may passl in indirect heat exchange with the enclosed pressure tight chamber.

Inasmuch as it is desirable in most high temperature cracking and conversion operations involving autothermic or oxidative cracking, to preheat the reactant streams to high preheat temperatures and to conserve heat within the processing unit, it is desirable to utilize recuperative heating, so the gaseous product stream gives up heat to the reactant streams. Thus, it is a desirable feature of the present invention to utilize extended pipe coils for accommodating the introduction of the hydrocarbon or other gaseous reactant stream and the air stream. The present invention provides heat exchange coils in an outlet gas passageway of annular shape, which, as noted, is positioned between an enclosing chamber and an i'nnerftubular member which in turn accommodates and encloses the reaction section. The reactant stream coils are also preferably placed in a continuons double helical coil arrangement maintained" directly within the annular gas passageway space, .so that there is an increased mass velocity for the outgoing product gas stream which gives rise to an`i1jicreased*heat exchag'e .to the gaseous -reactant streams in the'pi'pe coils.`

`VThe present reactor also maintains in combination .therewith a spaced and circumscribing heating chamber which provides an annular heating .space to pass hot gases in external heat exchange relationship with the enclosed pressure .tight chamber., with the external'chamber being arranged 4so that it-may be closed and in- Sllltdf T1111? providing by means f a' SealedV spaceand insulating'material the very eicient insulation of thev internal conversion chamber. The external heating chamber may provide high temperature heating for use in eifecting the starting-,up of a particular reaction within the reaction chamber, for example, in autothermic cracking, reaction and conversion temperature begreachedby heat exchange to the reactant streams introduced through the pipe coils and reaction chamber. Also, if desired .in A l t eY cracling or other conversion reactions fory nixed gaseous streams, continuous external heating may be provided around the enclosed conversion chamber during its operation.

A, pregerredV embodiment ofthe present type of reactor also has at Vleast one removable end to the pressure tight .conversion chamber such that the reactant stream pipe coils andthe inner 'tubular member maybe readily placed and assembled vor alternatively removed for :maintenance purposes.

The construction and arrangement or the improved 4apparatus of this invention, as well as other advantageous features, for effectively and enficientlyd carrying out high temperature gas mixing and conversion operations will be morev clearly shown upon reference tothe accompanying Vdrawing and the following description there- Referring now to the drawing, there is indicated an elongated enclosed chamber I, having in this particular embodiment, a removable. lower end orhead portion 2 which is.connected to the main portion of the chamber by means of bolted anges 3 and 4. The chamber l is of a pressure tight construction and of a refractory metal or alloy suitable for high temperatureconversion operations, such' .as theautothermic .4 cracking of ethane or propane at temperatures of the order of 1600 0r 1700* F. Alternatively, steel or alloy materials may be lined with a suitable insulating or heat resistant material. Positioned internally within chamber l is a high temperature resistant refractory tubular member 5 and the latter is preferably spaced concentrically in the chamber so as to provide an annular-shaped gas passageway 6 therebetween. For purposes of easy assembly, the inner tubular member 5, is as indicated, supported on suitable brackets .or vlugs 1 lwhich are attached to the inside Aof the lower head 2. Thus, the upper larger portion of chamber l may be pulled up and removed from around the tubular member 5 and the Aother internal portions of the appara# tus.

' Gas inlet conduits 8 and 9 are shown passing through the lower 'head 2 and into the interior of chamber :l in '.crder that they may discharge a vmixed :gaseous stream into the central reaction sec-tierras will hereinafter be described. Suitable pvac-lging glands l0 and Il are provided for each of the inlet conduits in order that a desired'superatmospheric pressure may be maintained within the interior chamber I. Each of the reactant stream inlet conduits or pipes 8 and Yil pass upwardly through .the .annular Ygas passageway ;6 and around the tir-mer .tubular member 5. to 'the upper end thereof, where they connect .with internally positioned conduits SF2 and L3 which pass downwardlyfthrough `the .body of the tubular member 5. and iconnect Ywith -a mixing .chamber M. pipes or conduits B. and. lil pass in a 'helical coil arrangement around the tubular member 5^, with the conduits winding in a parallel double helical' coil until they reach the upper portion of `the member 5. This arrangement provides for preheating Ythe reactant stream iin each of the conduits 3 and 9 by heat exchange with Ythe vresulting product stream which passes down-vvardlyv for Y.effecting the continuous autotherrnic :cracking of a low molecular weight hydrocarbon stream,

` suchV as propane, to provide. a relatively 4low density resulting gas, which; may bei utilized as a .fuel vgas forv supplementing a normal .gas .supply for peak load conditions, 'or to provide gas Ywhich may be mixed with natural or manufacturedgas beine Sent Out by eas'sucplvns companies.

an ideal autothermic process, the air and hydro.- Carbon reactant Streams nass tbreush heat .exchange means whereby vthey are preheated-b the product gas to reach a suitable reaction termx perature., and there. is. little. or r1.0. 1.0.5.5 0f heat from the System. with. the. heet @vel-ved by the.

` stream issuing vfrom the 'reactor section IB.. The

relatively narrow gas..passageway 6. provides; a

high massvelocity forfthe product stream 'and Preferably, eachV of the provides a relatively high heat transfer coeiicient in the exchange of heat from the product stream to the reactant streams in the helical pipe coils. Thus, preheated propane is introduced from the coiljle'into the enclosed conduit or passageway I2 within the body of the tubular member 5, and a preheated air stream is introduced into the conduit I3 which also extends longitudinally through the body of the tubular member 5. y

As previously noted, the reactant streams are introduced from the internal tubes or conduits I2 and I3 into a, mixing chamber I4, however, in accordance with a preferred form of a gas mixing reactor of this type, the gas streams are preferably introduced into the chamber I4 in an opposing manner and with a high velocity. Thus, venturi shaped or otherwise restricted ports., such as 2@ and 2|, introduce vthe streams into a small diameter mixing throat I9 which in turn passes the resulting mixed gases at high velocity through a flared opening 22 directly into the elongated reaction zone I8. This reaction zone IB is formed by an elongated hollow portion within the center of the tubular member and an open upper end suitable to discharge into the upper end of the interior of chamber I, whereby the resulting product stream must reverse its ilow and pass downwardly through the restricted annular shaped gas passageway 5. In the autothermic cracking operation, the air burns a portion of the hydrocarbon stream, or in this instance propane, in order to provide high temperature combustion products which in turn effect the cracking of the remaining portion of the propane stream, with resulting relatively large quantities of ethylene, propylene, and hydrogen, and with little or no significant formation or undesirable products.

The air to hydrocarbon ratio may of course be Varied to change the resulting product stream and to vary the B. t. u. value of the resulting gas. In the mixing chamber I4 and in the lower portion of the reaction section I8, the gas mixture may rise to a temperature of the order of l900 F. before the combustion reactions are overtaken by cracking reactions which reduce the temperature to the order of 1500 F. The mixing chamber and the mixing throat thereof is designed to provide a high degree of turbulence so that there is rapid relatively homogeneous mixing of the reactant stream. The reactor of the present design may of course utilize a refractory type of packing material within the elongated reaction section I8 where it is desirable to provide further mixing and turbulence of the stream passing up` wardly through the interior zone and prior to reaching the annular-shaped passageway t. Also, if desired, a suitable deilector plate, such as alloy plate 23, spaced above the top of the reaction section I8, may be used to prevent the direct impingement of the hotgaseous product stream against the top of the chamber I and to deflect the resulting .product stream downwardly through the gas passageway 6.

It is a particular feature of the present autothermic reactor to utilize an enclosing or circumscribing heating chamber 24A spaced around chamber I. The external chamber 24 is spaced concentrically around chamber I to provide an annular heating section 25. A continuous burner ring 26 is positioned within the lower portion of heating section 25 and is supplied with a suitable fuel gas by way of line 21 and control valve 28. Thus, high temperature vcombustion gases may be` provided withinthe heating section 25 and pass upwardly around and in heat exchange relationship with the inner chamber I so .that the'interior of the latter may be brought up to a high temperature suitable to start the autothermic cracking reaction. Combustion and vfuel gases from the heating chamber 25 may be discharged by way of an outlet stack 29. Air suitable to sustain burning of fuel gas from the burner ring 26 may be supplied by way of ports or openings 30 in the lower portion of the chamber 24 and by means of movable or slidable doors 3 I, which are placed over the ports 33,

when the burner ring 26 is not in operation. One or more layers of heatretaining insulation'is used externally aroundthe chamber 24 and around the lower head 2 of the conversion chamber. Preferably, the covering insulation is in two sections with a joint or splice somewhere near the line of the iianges 3 and 4 so that theenclosing heating chamber 24 may be lifted up and removed nal fcircumscribing heating section around the conversion chamber.` For starting up purposes, a suitable fuel gas may be burned inthe heating section 25 and a high temperature provided for heating up the interior of the conversion chamber I and preheating the reactant streams in the coils i5 and I'I so that they may reach a temperature sufficient to sustain the autothermic reaction. This arrangement eliminates the necessity of a sparking vcoil or other igniting means placed within the body of the reactor itself to start or initiate combustion of the mixed gas reactant streams in the mixing chamber I4 or the lower portion of the reaction section IB. During normal operation of the autothermic reactor, the stack or vent 29 may be closed off and the inner heating space 25 provide a substantially dead-air space as added insulation for the conversion chamber I, being in addition tol the external heating chamber 24 and insulating material 32. fuel gas may lbe continuously burned from the ring 26 and thus maintain a continuous flow of hot combustion gases externally along the wall of chamber I so that the coils I6 and I1 internally within the chamber I but closely adjacent to the wall I are insured of having a desired high vtemperature and a desired preheating of the reactant gas streams prior to their being intro-` duced into the mixing chamber I4. Thus, the present apparatus provides not only a compact design .and arrangement for a recuperative type of reactor having the hot product gases passing in heat exchange with the reactant streams, but means for providing an external source of heat to use in starting-up the rconversion process or to maintain ideal highly efficient operating conditions.

The present drawing of the improved apparatus is of course diagrammatic and minor modi--V cations may be made in connection with various details of the unit. Additional or auxiliary Lfeatures .may ofcourse be added to the unit, such as for example, Athermo-well connections may be utilized in connection with the reactor in order to connect suitable thermocouples with" Alternately, a small quantity ofV various internal zones in the apparatus for determining critical temperatures during the operation of the unit. The use of suitable pack'- ing material, such as heat resisting porcelain Raschig rings within the elongated reaction seotion I8 has been hereinbefore noted, however., it is also within the scope of the .present invention to utilize a catalytic material within the reaction section, whereby there is aid in effecting a particular conversion operation within the present improved form of gas mixing apparatus.

We claim as c-ur invention:

1. A recuperative type `of reactor comprising in combination, an enclosed elongated chamber having a refractory tubular member positioned concentrically and longitudinally therein, the refractory walls of said tubularv member being spaced from said chamber and forming an annular-shaped gas passageway therebetween, said tubular member being open at one end and lhaving a relatively thick refractory closure at its opposite end spaced from the corresponding end of Vsaid chamber with an .elongated axially positioned inner hollow portion forming la reaction section therein, said reaction `section communieating through the open end of Ysaid tubular member directly with the interior of said enclosed chamber, reactant stream inletsv connecting with said elongated chamber adjacent the closed end of said tubular member, pipe 'coils extending from said inlets around said tubular member and positioned within said annular gas passageway, said coils extending to the end of said tubular member and connecting with internal conduits embedded in and extending longitudinally throughA the refractory walls of said tubular member to the inlet ports of a mixing chamber formed within said relatively thick end closure of the tubular member, said ports connecting to and discharging into a mixing throat of said mixing chamber and said mixing throat discharging a resulting mixed gaseous stream throughsaid mixing chamber into said inner reaction sectionjof said tubular member, ka gas outlet from said chamber at the inlet end thereof, an insulated heating chamber spaced from and circumscribing said enclosed chamber and providing an external annular heating section, a gas burner and fuel supply means at one end of said heating section, adjustable air inlet means through said heating chamber adjacent said burner, and flue gas outlet means from 'said heating chamber at an end thereof away froml said gas. burner whereby hot combustion gases pass in heat exchange iiow over said enclosed chamber.

2. The reactor of claim 1 further characterized in that said pipe coils extending from said inlets around said tubular members are positioned in a double helical coil arrangement coextensive for substantially the full length of said inner tubular member. Y.

v3. The reactor of claim 1 further characterized in thatrsaid enclosed elongated Ychamber `is constructed of a heat resistant metal permitting Vthe substantiallyr apid1 vtransfer of heat: from said external heating section into the interior, thereof for preheating said reactant streams within said pipe coils. l

4. A combination recuperative and'externally heated reactor for -eecting high temperature cracking of reactant streams, comprising in combination, an elongated vertically disposed pressure tight conversion chamber having a removable lower portion, an elongated refractory tubular member'positioned c'oncentrically and longitudinally within said Vchamber 5in a manner forming an annular-shaped gas passageway with the inner wall of said .conversion chamber, said tubular member having a Vrelatively thick end closure spaced from said removable lower portion of the chamber, the tubular member being vopen at its opposite end and providing an elongated axially positioned inner hollow portion forming a reaction section, said reaction section being open to the inner portion'of said chamber and to said annular shaped gas passageway through the open end of said tubular member, a reactant stream inlet and an air stream inlet passing through said removable end .portion of "said elongated chamber, 'each inlet separately connecting with helical pipe coils extending around said elongated tubular member and positioned within said annular-shaped gas passageway, said helical coils arranged in parallel double coil arrangement coextensive to the end of said tubular member having the opening therethrough, with said helical coils separately connecting with internal conduits embedded in and extending longitudinally through the walls of said tubular member into a mixing chamber formed within said relatively thick end closure of the tubular member, said mixing chamber being positioned adjacent to and communicating with 'the inner end of said reaction section within said tubular member, said mixing chamber having restricted inlet ports connecting with said internal conduits and discharging in an opposing manner into a small diameter mixing throat positioned concentrically within said mixing chamber, whereby said mixing throat Aand said mixing chamber discharge a resulting mixed gaseous stream directly into and axially through said reaction section, a product gas outlet from the removable end portion of said closed chamber and adjacent the gas inlets therethrough, whereby the resulting gaseous product stream rom said reaction section reverses its iiow and passes through said gas passageway around said elongated tubular member and lthrough the inlet end of said closed chamber, an insulated heating chamber spaced from and circumscribing said enclosed pressure tight chamber, said heating chamber forming thereby an external annular heating section around said enclosed chamber, a continuous burner ring within the lower end of said heating section and air and fuel gas supply means through said heating chamber to said burner ring, ue gas outlet from said heating chamber at the upper end thereof whereby hot gases flow around substantially theY full length oi said enclosed chamber in heat exchange therewith, adjustable andinovably positioned inlet doors through the heating chamber at a zone adjacent said continuous burner ring to provide means for adjustably introducing air to the latter.

5. A reactor comprising an elongated chamber, a tubular member positioned concentrically and longitudinally in the chamber and having a relatively thick rerractoiybody portion spaced from the chamber walls and a relatively thick refractory end closure spaced from the corresponding end of the chamber, the opposite end of the tubular member being open to' provide communication between the interior of said member and the annular space between said body portion and said chamber, reactant stream inletsV extending through said endv of the chamber, pipe coils connected to said inletsand poi References Cited in the file of this patent UNITED STATES PATENTS Name Date Number McHenry Sept. 28, 1915 Number Number 5,510 lo of 1927 Name l Date Cicali Jan. 28, 1930 Chilowsky May 6, 1930 Leprestre etal May 18, 1943 Starr Aug. 3, 1948 Deanesly Nov. 14, 1950 FOREIGN PATENTS Country Date Australia Jan. 11, 1927k 

5. A REACTOR COMPRISING AN ELONGATED CHAMBER, A TUBULAR MEMBER POSITIONED CONCENTRICALLY AND LONGITUDINALLY IN THE CHAMBER AND HAVING A RELATIVELY THICK REFRACTORY BODY PORTION SPACED FROM THE CHAMBER WALLS AND A RELATIVELY THICK REFRACTORY END CLOSURE SPACED FROM THE CORRESPONDING END OF THE CHAMBER, THE OPPOSITE END OF THE TUBULAR MEMBER BEING OPEN TO PROVIDE COMMUNICATION BETWEEN THE INTERIOR OF SAID MEMBER AND THE ANNULAR SPACE BETWEEN SAID BODY PORTION AND SAID CHAMBER, REACTANT STREAM INLETS EXTENDING THROUGH SAID END OF THE CHAMBER, PIPE COILS CONNECTED TO SAID INLETS AND POSITIONED IN SAID ANNULAR SPACE AROUND SAID BODY PORTION OF THE TUBULAR MEMBER, A MIXING CHAMBER FORMED WITHIN SAID RELATIVELY THICK END CLOSURE AND DISCHARGING INTO THE INTERIOR OF THE TUBULAR MEMBER, GAS CONDUCTING CONDUITS EMBEDDED IN SAID BODY PORTION OF THE TUBULAR MEMBER AND CONNECTING SAID PIPE COILS WITH SAID MIXING CHAMBER, AND A GAS OUTLET FROM SAID END OF THE FIRS-MENTIONED CHAMBER. 